Various high temperature materials have been developed for use in gas turbine engines. Cobalt-base and nickel-base superalloys have found wide use in the manufacture of gas turbine engine components such as nozzles, combustors, and turbine vanes and blades. Other materials, including niobium-based alloys, have been considered for the high temperature regions of gas turbine engines, such as the turbine and exhaust sections. For example, on the basis of promising acceptable levels of fracture toughness and creep resistance, silicide-based composites toughened with a niobium-based metallic phase (e.g., NbTiHfCrAlSi solid solution) have been investigated for applications where blade surface temperatures may exceed 1200 C. However, niobium and niobium-containing compositions generally do not exhibit a sufficient level of oxidation resistance at elevated temperatures. For this reason, niobium-containing materials intended for high temperature applications have typically required an oxidation-resistant coating, particularly if operating temperatures will exceed about 800 C. Commercially-available fusion coatings based on, in weight percent, Si-20Fe-20Cr have been proven effective in improving the oxidation resistance of niobium-base alloys. However, the high-temperature fusion (reaction bonding) process can be detrimental to the material, depending on its nature. In addition, the Si-20Fe-20Cr alloy has not proven to be suitable as an oxidation-resistant coating for silicide composites with a niobium-based reinforcement phase.
Therefore, it would be desirable if a silicide-based composite were available that exhibited improved oxidation resistance at temperatures of up to 1200 C., to enable such a material to be used in the hot section (turbine and exhaust) of a gas turbine engine without an oxidation-resistant coating.